1. Field of the Invention
The present invention relates to a liquid ejection head for ejecting liquid such as ink.
2. Description of the Related Art
A liquid ejection head for ejecting liquid such as ink is generally mounted onto a liquid ejection device for recording an image on a recording medium by ejecting the liquid such as ink. As a mechanism for causing the liquid ejection head to eject ink, there is known a mechanism using a pressure chamber which is shrinkable in volume by a piezoelectric element. In this mechanism, the pressure chamber shrinks due to the deformation of the piezoelectric element to which a voltage is applied, and thus the ink inside the pressure chamber is ejected from an ejection orifice formed at one end of the pressure chamber. As a liquid ejection head including such a mechanism, there is known a shear mode liquid ejection head in which one or two inner wall surfaces of the pressure chamber are formed of the piezoelectric element, and shear deformation of the piezoelectric element is caused by voltage application, to thereby shrink the pressure chamber.
Regarding liquid ejection devices for industrial applications, there is a demand for use of high viscosity liquid. In order to eject high viscosity liquid, a large ejection force is required for the liquid ejection head. To satisfy this demand, there has been proposed a liquid ejection head called a Gould type, in which the pressure chamber is formed of a piezoelectric member having a circular or rectangular sectional shape. In the Gould type liquid ejection head, the piezoelectric member is uniformly deformed in the inward and outward directions (radial direction) about the center of the pressure chamber. In this manner, the pressure chamber expands or shrinks. In the Gould type liquid ejection head, the entire wall surface of the pressure chamber deforms, and this deformation contributes to the ink ejection force. Therefore, as compared to the shear mode liquid ejection head in which one or two wall surfaces are formed of the piezoelectric element, a larger liquid ejection force can be obtained.
In order to obtain a higher resolution in the Gould type liquid ejection head, it is necessary to arrange a plurality of ejection orifices in higher density. To meet this necessity, it is necessary to arrange the pressure chambers corresponding to the respective ejection orifices in higher density. Japanese Patent Application Laid-Open No. 2007-168319 discloses a method of manufacturing a Gould type liquid ejection head, which is capable of forming the pressure chambers in high density.
In the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319, first, a plurality of grooves all extending in the same direction are formed in each of a plurality of piezoelectric plates. After that, the plurality of piezoelectric plates are laminated so that the grooves are uniformly directed, and are cut in a direction orthogonal to the direction of the grooves. The groove part of the cut piezoelectric plate forms an inner wall surface of the pressure chamber. After that, in order to separate the respective pressure chambers, the piezoelectric member present between the pressure chambers is removed to a certain depth. On an upper side of the piezoelectric plate having the completed pressure chambers, a supply path plate and an ink pool plate are connected, and on a lower side thereof, a printed circuit board and a nozzle plate are connected. In this manner, the liquid ejection head is completed. With this manufacturing method, the pressure chambers can be arranged in a matrix, and hence the pressure chambers can be arranged in high density. Further, with this manufacturing method, because forming a groove in the piezoelectric plate is better in workability than opening a hole in the piezoelectric plate, the pressure chambers can be formed with high accuracy.
On the other hand, in the Gould type liquid ejection head, it is known that air bubbles generated inside the pressure chambers cause such an ejection trouble that the ink cannot be ejected from the ejection orifices, and countermeasures against this ejection trouble are required. Japanese Patent Application Laid-Open No. S61-249760 and Japanese Patent Application Laid-Open No. 2006-95878 each disclose a measure of degassing air bubbles and dissolved oxygen in the ink inside the pressure chamber even during printing in order to prevent accumulation of air bubbles in the ejection orifice (nozzle).
In the liquid ejection head manufactured by the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319, the plurality of pressure chambers are arranged while being separated from each other with a space provided therebetween. That is, the wall portions forming the respective pressure chambers are independently formed. Therefore, particularly when the length (height) of the pressure chamber is increased in order to eject high viscosity liquid (in other words, in order to increase the liquid ejection force), the rigidity of the liquid ejection head is lowered. When the rigidity is lowered, the pressure chamber may easily break, which may lead to difficulty in liquid ejection.
Further, the measures disclosed in Japanese Patent Application Laid-Open No. S61-249760 and Japanese Patent Application Laid-Open No. 2006-95878 cannot be effectively applied to the Gould type liquid ejection head in which the plurality of ejection orifices (pressure chambers) are two-dimensionally arranged.